This is sort of true.
It's more akin to tripwires that get installed upon the initial trauma.
I read a quote on PTSD recently that described it well. "People think PTSD is not letting go of the past when in reality it's the past not letting go of the sufferer."
Imagine an imprint made in the psyche, encoded on the brain at the onset/initial response to trauma.

Professionals in the field of trauma research are beginning to describe it as a brain injury.
Because there are physical changes that take place in the brain. The prefrontal cortex that deals with higher cognition, for example, shuts down. Think of it like any other physical injury, banging your elbow on something, or burning yourself. When you touch the affected area it's tender and if it's really painful, it's going to send strong signals immediately to the brain causing a pain response. It's similar with PTSD (except that the cause is psychologically induced) when one of the trip wires is crossed and something triggers the fight/flight/freeze response (re-activating that original imprint as if it's recurring) all sorts of physiological and psychological processes follow as a direct result.

I'll be sharing my own experiences with this here at some point.